Accelerometers may be categorized as open-loop accelerometers or closed-loop accelerometers. Open-loop accelerometers have proof masses that are displaced in the presence of inertial forces, and an amount of the displacement is measured to determine the acceleration value. By contrast, closed-loop accelerometers have proof masses that are maintained in a fixed position by a servo system. The force generated by the servo system necessary to maintain that position is measured to determine an acceleration value.
Conventional closed-loop accelerometer designs may utilize a capacitive pick-off to detect the displacement of a proof mass. Electrically conductive material (e.g., a capacitor plate) may be deposited on the upper surface of the proof mass, and similar electrically conductive material may be deposited on the lower surface of the proof mass. An acceleration or force applied along the sensitive axis of the accelerometer causes the proof mass to deflect either upwardly or downwardly causing the distance (e.g., a capacitive gap) between the pick-off capacitance plates and the upper and lower excitation rings to vary. This variance in the capacitive gap causes a change in the capacitance of the capacitive elements, which is representative of the displacement of the proof mass along the sensitive axis. The change in the capacitance may be used as a displacement signal and applied to a servo system that includes one or more electromagnets (e.g., a force-rebalancing coil) to return the proof mass to a null or at-rest position.